JP5298451B2 - Sliding structure - Google Patents

Description

  The present invention relates to a sliding structure including a pair of sliding members in which an amorphous carbon film is formed on a sliding surface of one sliding member among a pair of sliding members that slide relative to each other, in particular. The present invention also relates to a sliding structure including a lubricant containing an organomolybdenum compound between the pair of sliding members.

  Conventionally, sliding members are used in various devices such as engines and transmissions in automobiles. There, various research and developments are underway to reduce the sliding resistance of the sliding member to reduce energy loss and to meet future fuel efficiency regulations for protecting the global environment.

  For example, as one of such research and development, there is a technique for coating the sliding surface of the sliding member in order to improve the wear resistance of the sliding member and obtain low friction characteristics. In recent years, amorphous carbon materials such as diamond-like carbon (DLC) have attracted attention as this coating material. The film (amorphous carbon film) formed of the amorphous carbon material is a hard film mainly composed of carbon, and the carbon of the hard film also acts as a solid lubricant. It is a coating that can achieve both resistance and high wear resistance.

  On the other hand, the lubricant (lubricant, grease) supplied to the sliding surface of the sliding member when sliding the sliding member greatly affects the sliding characteristics of the sliding member. It is very important to select a lubricant so as to obtain an optimum sliding structure in consideration of the material, surface roughness, usage environment, and the like.

  For example, as such an example, a pair of sliding members in which a DLC film (amorphous carbon film) is formed on the surface of a base material, and molybdenum didithiophosphate (Mo--) on the sliding surfaces of the pair of sliding members. A sliding structure including a lubricant containing an organic molybdenum compound such as DTC) or molybdenum dithiocarbamate (Mo-DTP) as a metal friction modifier has been proposed (see Patent Document 1).

  According to this sliding structure, at the time of sliding, the organic molybdenum compound becomes molybdenum disulfide between the sliding surfaces. Since the molybdenum disulfide acts as a solid lubricant, the sliding characteristics of the sliding member can be improved.

JP-A-2005-060416

  By the way, when the amorphous carbon film is formed by chemical vapor deposition (CVD), droplets and the like are not generated on the surface as compared with those formed by physical vapor deposition (PVD). In addition, the surface roughness of the amorphous carbon coating can be lowered, and the friction coefficient of the sliding member and the partner attacking property against the partner member can be reduced. However, when an amorphous carbon film is formed by CVD, a hydrogen element may be contained in the amorphous carbon film. In such a case, as the sliding member slides, The amorphous structure of the amorphous carbon film and the organomolybdenum compound in the lubricant may chemically react to cause wear of the amorphous carbon film.

Specifically, as shown in FIG. 6, a part of the organomolybdenum compound is thermally decomposed by frictional heat between the sliding members, and molybdenum trioxide (MoO ₃ ) that is an oxidation catalyst is generated. In the environment where the molybdenum trioxide is present, when the sliding member comes into contact at a high surface pressure and a high dynamic speed, the hydrogen element in the amorphous carbon film is desorbed from the film by a kind of reduction action, The strength of the amorphous carbon film may be reduced. In this way, the carbon from which the hydrogen element is desorbed becomes the active site, and the carbon that has become the active site chemically reacts with molybdenum trioxide and desorbs from the film, and carbon monoxide or carbon dioxide gas and Become. Furthermore, the carbon desorbed by the reaction causes the carbon bonded to the desorbed carbon to become an active site, chemically react with molybdenum trioxide and desorb from the film, and carbon monoxide or carbon dioxide It becomes gas. Thus, it is considered that the abrasion of the amorphous carbon coating proceeds by repeating the chemical reaction in a superimposed manner on the surface of the amorphous carbon coating.

  The present invention has been made in view of such a problem, and the object is to use a lubricant containing an organic molybdenum compound in an amorphous carbon film containing a hydrogen element. Another object of the present invention is to provide a sliding structure capable of suppressing the wear of the amorphous carbon film due to a chemical reaction between the amorphous carbon film and the organic molybdenum compound.

  The inventors of the present invention focused on a thermal decomposition reaction in which molybdenum trioxide is generated from an organomolybdenum compound by conducting many experiments and studies to solve the above-described problems. The inventors have added a predetermined additive to the lubricant so that the phenomenon of the thermal decomposition reaction does not occur, thereby suppressing the detachment of hydrogen element from the amorphous carbon film, and the amorphous material. The knowledge that the chemical reaction which a carbonaceous film wears out can be suppressed was acquired.

  The present invention is based on the above-mentioned new knowledge obtained by the present inventors, and the present invention is based on the fact that the sliding surface of one sliding member of the pair of sliding members sliding relative to each other is hydrogenated. The sliding structure includes at least a pair of sliding members on which an amorphous carbon film containing an element is formed, and a lubricant that is present between the pair of sliding members and includes at least an organic molybdenum compound. The lubricant further includes a copper-based additive.

  According to the present invention, it is possible to suppress the formation of molybdenum trioxide from the organic molybdenum compound by adding a copper-based additive to the lubricant present between the sliding surfaces of the pair of sliding members. it can. That is, until now, organic molybdenum was thermally decomposed by frictional heat generated when the sliding member was slid to produce molybdenum trioxide. In the present invention, a copper-based additive is added to the lubricant. By containing, heat generation due to frictional heat can be suppressed, and generation of molybdenum trioxide due to thermal decomposition of the organic molybdenum compound can be suppressed. As a result, the desorption phenomenon of the hydrogen element of the amorphous carbon film by molybdenum trioxide is suppressed, and the wear of the amorphous carbon film due to a chemical reaction can be reduced.

  In the present invention, “a pair of sliding members that slide relative to each other” refers to a sliding member in which at least one sliding member slides relative to the other sliding member. The movement refers to sliding by linear movement, rotational movement, or a combination of these movements.

  The amorphous carbon film is a film (DLC film) made of so-called DLC (diamond-like carbon), and the amorphous carbon film uses sputtering, vacuum deposition, ionization deposition, ion plating, or the like. The film may be formed by physical vapor deposition (PVD), may be formed by chemical vapor deposition (CVD) utilizing plasma treatment, or may be formed by a combination of these methods. Also good. The amorphous carbon coating may contain additional elements such as Si, Cr, Mo, Fe, and W, and the surface hardness of the coating is adjusted by adding such elements. You can also.

  Further, the surface hardness of the amorphous carbon film of the sliding member is preferably in the range of Hv1000 to Hv4000. When the surface hardness is less than Hv1000, the amorphous carbon film is easily worn, and when it is Hv4000 or more In this case, the adhesion between the amorphous carbon coating and the base material of the sliding member is reduced. Further, the film thickness of the coating of the sliding member is preferably 0.1 μm or more. If the film thickness is smaller than this thickness, the film is worn away at the time of sliding, and the desired effect is obtained. Can't get. Further, in order to improve the adhesion of the amorphous carbon coating between the substrate and the amorphous carbon coating, it is selected from Ta, Ti, Cr, Al, Mg, W, V, Nb, and Mo. An intermediate layer made of one or more metal elements may be formed.

  The copper-based additive according to the present invention is preferably an organic copper compound, such as a copper-amine complex, a copper-succinimide complex, a copper salt of an organic acid, a copper salt of an alcohol, or a copper dialkyldithiocarbamate (Cu- DTC) or copper dithiophosphate (Cu-DTP) can be mentioned. As a more preferred embodiment, the copper-based additive according to the present invention is copper dithiophosphate (Mo-DTP).

According to the present invention, by containing copper dithiophosphate (Cu-DTP) in the lubricant, the sliding member (the other sliding member) on the other side of the sliding member on which the amorphous carbon film is formed is slid. It is possible to generate a film having excellent heat dissipation and excellent triploidy properties including a copper-based material such as copper sulfide (Cu _x S _y ) or copper phosphate (CuPO ₄ ) on the moving surface.

  That is, not only the copper contained in the copper dithiophosphate contained in the lubricant, but also the thermal decomposition of the organomolybdenum compound (molybdenum trioxide) by forming a film made of a copper-based material on the sliding surface, which is the heat generation point. The effect of suppressing the generation of can be further exhibited. As a result, it is possible to further suppress the wear of the amorphous carbon film due to a chemical reaction.

  Specific examples of such copper dithiophosphate (Cu-DTP) include, for example, copper diisopropyldithiophosphate, copper diisobutyldithiophosphate, copper dipropyldithiophosphate, copper dibutyldithiophosphate, copper dipentyldithiophosphate, copper dihexyldithiophosphate, Dialkyldithiophosphate copper having a linear or branched alkyl group having 3 to 18 carbon atoms, such as copper diheptyldithiophosphate and copper dioctyldithiophosphate; Carbon number such as copper diphenyldithiophosphate and copper ditolyldithiophosphate Examples thereof include ((alkyl) aryl) copper dithiophosphate having 6 to 18 aryl or alkylaryl groups, and these can be used alone or in admixture of two or more.

  Further, the organic molybdenum compound contained in the lubricant includes molybdenum-amine complex, molybdenum-succinimide complex, molybdenum salt of organic acid, molybdenum salt of alcohol, molybdenum dialkyldithiocarbamate (Mo-DTC) or molybdenum dithiophosphate. (Mo-DTP) etc. can be mentioned, As a more preferable aspect, the organomolybdenum compound concerning this invention is molybdenum dialkyl dithiocarbamate (Mo-DTC) or molybdenum dithiophosphate (Mo-DTP).

According to the present invention, molybdenum disulfide (MoS ₂ ) is formed on the surface of the other sliding member by using molybdenum dialkyldithiocarbamate (Mo-DTC) or molybdenum dithiophosphate (Mo-DTP) as the organic molybdenum compound. The molybdenum sulfide is formed on the sliding surface as a solid lubricant film. As a result, in addition to suppressing chemical wear of the amorphous carbon film formed on the sliding surface of the sliding member, wear of the sliding member due to mechanical contact between the sliding surfaces is further suppressed. can do.

  In particular, in consideration of versatility, cost, etc., the organomolybdenum compound contained in the lubricant is more preferably molybdenum dialkyldithiocarbamate (Mo-DTC), and the structure of the alkyl group in the molecule varies depending on the production method. For example, specific examples of molybdenum alkyldithiocarbamate include, for example, molybdenum dibutyldithiocarbamate, sulfurized dipentyldithiocarbamate, sulfurized dihexyldithiocarbamate, sulfurized diheptyldithiocarbamate, sulfide dioctyldithiocarbamate, dinonyldithiocarbamate. Molybdenum, molybdenum didecyl dithiocarbamate, sulfurized diundecyl dithiocarbamate, sulfurous molybdenum dododecyldithiocarbamate, molybdenum ditridecyldithiocarbamate, and the like.

  Moreover, as for the sliding structure which concerns on this invention, it is more preferable that the said copper dithiophosphate (Cu-DTP) contains 0.05-0.5 mass% with respect to the said lubricant. That is, according to the present invention, the wear amount of the amorphous carbon coating can be reduced by setting the content of copper dithiophosphate to the lubricant in the above range. That is, when copper dithiophosphate is less than 0.05% by mass with respect to the lubricant, it is not sufficient to suppress the thermal decomposition action of the organic molybdenum compound, and the wear amount of the amorphous carbon coating tends to increase. It is in. Even when the amount of copper dithiophosphate is more than 0.5% by mass with respect to the lubricant, it is difficult to expect further suppression of the thermal decomposition action of the organic molybdenum compound, which is not economical.

  The lubricant base oil is not particularly limited as long as it contains the above-described additives, and includes mineral oil and synthetic oil. Such lubricants can be appropriately added with an antioxidant, an antiwear agent, an extreme pressure agent, a friction modifier, a metal deactivator, a detergent, a rust preventive, an antifoaming agent, and the like. It should be noted that, in place of the lubricant, for example, even if the grease further includes a thickener dispersed in a base oil containing an organic molybdenum compound and a copper-based additive, the effect of suppressing the thermal decomposition of the organic molybdenum compound described above is obtained. It is done.

  In addition, examples of the lubricant supply mechanism include a circulation lubrication mechanism, a mist lubrication mechanism, and an oil bath lubrication mechanism using an oil bath. The lubricant may be supplied between the sliding members during sliding. If possible, it is not particularly limited.

  In the sliding structure according to the present invention, the other sliding member is more preferably a sliding member made of an iron-based material. According to the present invention, by using the other sliding member as an iron-based material, copper dithiophosphate reacts with the iron-based material to form a film made of a copper-based material on the sliding surface of the other sliding member. Furthermore, since the organic molybdenum compound becomes molybdenum disulfide and has good compatibility with the iron-based material, it is possible to suppress not only the wear of the iron-based material but also the wear of the amorphous carbon film. Further, the “iron-based material” referred to in the present invention may be either a steel-based material or a cast-iron-based material, and the material of the surface that contacts and slides the amorphous carbon coating is steel, or If it is an iron-type material, it will not specifically limit.

  According to the present invention, even when a lubricant containing an organomolybdenum compound is used on the sliding surface on which the amorphous carbon coating containing hydrogen element is formed, the hydrogen element and the organic carbon in the amorphous carbon coating are used. Abrasion of the amorphous carbon film due to a chemical reaction with the molybdenum compound can be suppressed.

Hereinafter, the present invention will be described by way of examples.
[Example]
(Sliding structure)
In the following, as shown in FIG. 1 (a), out of a pair of sliding members 10 and 20 that slide relative to each other, the sliding surface of the base material 12 of one sliding member 10 contains an amorphous element. The sliding member 10 on which the carbonaceous film 11 is formed, the other sliding member 20 that slides on the sliding surface of the sliding member 10, and the pair of sliding members 10, 20, A sliding structure 1 including an organomolybdenum compound and a lubricant 30 containing at least a copper-based additive was prepared. More specifically, as shown in FIG. 2A, a plate test piece 10A was prepared as one sliding member 10, a ball test piece 20A as the other sliding member, and a grease 30A as the lubricant 30. Details are shown below.

  1A is a conceptual diagram of the sliding structure according to the present invention, and FIG. 1B is a diagram for explaining a sliding state in the sliding structure according to the present invention. (a) is a figure for demonstrating the sliding structure which concerns on a present Example, (b) is for demonstrating the state of the plate test piece after the sliding which concerns on a present Example (after completion | finish of a friction test). (C) is AA 'sectional drawing of (b).

<Plate test piece>
As shown in FIG. 2 (a), as the base material 12A for forming the amorphous carbon coating 11A, the surface roughness is a 10-point average roughness Rz 0.1 μm, diameter 24 mm × thickness 7.9 mm, surface hardness Hv700. High carbon chromium bearing steel (SUJ2: JIS standard) is prepared, and the surface of this substrate 12A has a diameter of 24 mm and contains a hydrogen element so that the thickness is about 6 μm and the surface hardness is about Hv2000 by plasma CVD. A plate specimen 10A on which the amorphous carbon coating 11A (HT-DLC (thick film, highly reliable DLC: manufactured by Japan IT Corporation)) was formed was prepared.

<Ball specimen>
As shown in FIG. 2A, a spherical ball test of 10 mm in diameter, Rockwell hardness HRC62 (equivalent to Vickers hardness Hv700), material 100CR-6 (JIS standard: equivalent to high carbon chromium bearing steel (SUJ2)) A piece 20A was prepared.

<Grease>
As shown in FIG. 2A, a grease containing molybdenum dialkyldithiocarbamate (Mo-DTP) is prepared as a lubricant to be supplied between the plate test piece 10A and the ball test piece 20A. Further, a grease 30A containing 0.5% by mass of copper dithiophosphate (Cu-DTP) was prepared.

<Friction and wear test>
A wear test was conducted using an SRV testing machine. Specifically, grease 30A is supplied between the plate test piece 10A and the ball test piece 20A, and the surface pressure during sliding is 2.0 to 2.47 GMa between the plate test piece 10A and the ball test piece 20A. A load of 80 to 150 N is applied so that the frequency is 50 Hz, the sliding amplitude is 1.5 mm, the sliding speed is 0.15 mm / second, and the sliding time is 10 minutes. went. The temperature in the vicinity of the sliding portion of the plate test piece during sliding was also measured.

  The appearance of the sliding surface of the plate test piece was observed. The result is shown in FIG. As shown in FIGS. 2B and 2C, the wear depth along the arrow line A-A ′ of the sliding portion of the sliding surface of the plate test piece 10 </ b> A was measured. The result is shown in FIG. Further, in the same manner as in the above test, the load applied to the plate test piece 10A and the ball test piece 20A was changed to the load shown in FIG. 5, and the friction coefficient corresponding to each load was measured. The result is shown in FIG.

[Comparative Example 1]
The same plate specimen and ball specimen as in the example were prepared. The difference from the example is that the grease, which is a lubricant, did not contain copper dithiophosphate (Cu-DTC). And the friction abrasion test was done like the Example. The result of appearance observation is shown in FIG. 3B, the result of wear depth is shown in FIG. 4, and the measurement result of the friction coefficient in accordance with the load is shown in FIG. Similarly, the temperature near the sliding portion of the plate test piece during sliding was also measured.

[Comparative Example 2]
The same plate specimen and ball specimen as in the example were prepared. The difference from the examples is that the grease, which is a lubricant, did not contain molybdenum dialkyldithiocarbamate (Mo-DTC) or copper dithiophosphate (Cu-DTC). In the same manner as in the examples, a frictional wear test was performed, and a friction coefficient corresponding to the load was measured. The result is shown in FIG.

[Result 1]
As shown in FIG. 3B, wear marks were formed on the sliding surface of the plate test piece of Comparative Example 1. As shown in FIG. 4, the wear depth of the example was smaller than that of the comparative example 1. Furthermore, the temperature in the vicinity of the sliding portion of the plate test piece during sliding of the example was lower than that of Comparative Example 1.

[Result 2]
As shown in FIG. 5, the friction coefficients of Example 1 and Comparative Example 1 were similar, and were lower than those of Comparative Example 2.

[Discussion 1]
As shown in the result 1, the wear depth in the example was smaller than that in the comparative example 1. The temperature in the vicinity of the sliding portion of the plate test piece during sliding in the example compared with the comparative example 1 This is probably due to the fact that it was low. In other words, it is considered that the examples are due to the fact that the thermal decomposition of the organomolybdenum compound into molybdenum trioxide was suppressed by adding copper-based additive copper dithiophosphate to the grease. Furthermore, as shown in FIG. 1B, on the surface of the sliding member 20 (in this case, a ball test piece) on the other side of the sliding member 10 on which the amorphous carbon film 11 of the base material 12 is formed. A film made of a copper-based material made of copper sulfide (Cu _x S _y ) or copper phosphate (CuPO ₄ ) is formed from copper dithiophosphate (Cu-DTP), and a disulfide that acts as a solid lubricant on the film. By further forming a film made of molybdenum, thermal decomposition of molybdenum dialkyldithiocarbamate (Mo-DTC), which is an organic molybdenum compound, into molybdenum trioxide is suppressed, and wear due to a chemical reaction is suppressed. This is thought to be due to the suppression of excessive wear.

[Discussion 2]
As shown in Result 2, the value of the coefficient of friction in Example and Comparative Example 1 was smaller than that in Comparative Example 2 because molybdenum dialkyldithiocarbamate (Mo-DTC) was used as the organic molybdenum compound. As described above, it is considered that the molybdenum disulfide film was formed on the sliding surface. In addition, the sliding structure of the example has the same sliding coefficient as that of the comparative example 1 although the wear depth is smaller than that of the comparative example 1. However, it is not merely mechanically improved in wear resistance, and as described above, it suppresses thermal decomposition of molybdenum dialkyldithiocarbamate (Mo-DTC) to molybdenum trioxide and suppresses wear due to chemical reaction. It is thought.

  The sliding structure according to the present invention has a high sliding frequency, such as a sliding part of an engine combining a piston ring and a cylinder, a sliding part of a cam lifter combining a cam and a cam follower, and wear resistance and low friction. It is preferably used in an environment as required.

FIG. 1A is a conceptual diagram of a sliding structure according to the present invention, and FIG. 1B is a diagram for explaining a sliding state in the sliding structure according to the present invention. FIG. 2A is a diagram for explaining the sliding structure according to the present embodiment, and FIG. 2B is a state of the plate test piece after sliding according to the present embodiment (after completion of the friction test). FIG. 4C is a cross-sectional view taken along the line AA ′ in FIG. It is the photograph at the time of observing the external appearance of the sliding surface in which the amorphous carbon film of the Example and the comparative example 1 was formed, (a) is a photograph figure of the sliding surface of an Example, (b ) Is a photograph of the sliding surface of Comparative Example 1. The figure which showed the measurement result which measured the abrasion depth of the amorphous carbon film formed in the sliding surface of the Example and the comparative example 1. FIG. The figure which showed the result of having measured the change of the friction coefficient at the time of changing a load in the sliding structure of an Example and Comparative Examples 1 and 2. FIG. The figure for demonstrating the mechanism of abrasion generation by the chemical reaction of an amorphous carbon film.

Explanation of symbols

  1, 1A: sliding structure, 10: one sliding member, 10A: plate test piece, 11, 11A: amorphous carbon coating, 12, 12A: base material, 20: other sliding member, 20A: ball Specimen, 30: Lubricant, 30A: Grease

Claims (1)

Of the pair of sliding members that slide relative to each other, a pair of sliding members in which an amorphous carbon film containing a hydrogen element is formed on the sliding surface of one sliding member, and the pair of sliding members A sliding structure comprising at least a lubricant containing at least an organomolybdenum compound,
The other sliding member is a sliding member made of an iron-based material,
The lubricant contains molybdenum dialkyldithiocarbamate (Mo-DTC) or molybdenum dithiophosphate (Mo-DTP) as the organic molybdenum compound,
The lubricant is made of copper dithiophosphate (Cu-DTP) so that a film made of a copper-based material is formed on the sliding surface of the other sliding member when the pair of sliding members slide. sliding structure characterized in that it further contains an additive copper made.

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